Stereotactic Body Radiation Therapy (SBRT) has emerged as a novel approach for the local ablation of liver metastases. SBRT provides a conformal isodose distribution with a steep radiation dose gradient allowing much higher doses of radiation than conventional radiation therapy and conformal radiotherapy techniques to be delivered safely with high precision to focal liver metastases while minimizing the radiation dose to normal liver and adjacent organs. To achieve this, precise localization of the target during treatment is required which necessitates accounting for tumor motion. SBRT technology utilizes a number of techniques to accommodate for tumor and respiratory motion including motion-restrictive techniques such as frames and abdominal compression, as well as motion-compensating techniques such as active breathing control and tumor tracking. The motion-restrictive techniques can be difficult for some patients to withstand, limiting those patients from being able to receive treatment. The motion-restrictive techniques can also necessitate the use of wide margins. Rusthoven et al. found a gross tumor volume (GTV) to planning target volume (PTV) expansion of up to 15 mm necessary in the craniocaudal direction. Wide margins can result in irradiation of a substantial volume of normal liver, potentially increasing the risk of radiation-induced injury. Some studies suggest the motion-compensating approach of active breathing control can aid in reducing the margins required by motion-restrictive approaches, however, Korreman et al. suggest those reductions may only be applicable with the use of image-guidance between and within sessions.